Utility-scale wind turbines generally include a set of two or three rotor blades which radially extend from a rotor hub. The combined assembly of the rotor blades and the rotor hub is referred to as the rotor. The rotor blades aerodynamically interact with wind energy, creating lift and drag, which the rotor hub then translates into a driving torque. The driving torque is communicated from the rotor hub through a main shaft that is coupled to the rotor hub. The rotational torque is then distributed to one or more generators via a drivetrain, which in turn produce electric power to be processed and transmitted to an associated electrical grid. The main shaft, the drivetrain and the generators are all situated within a nacelle that is located on top of a tower.
The typical cost of manufacturing, implementing and maintaining a wind turbine is largely driven by the size and mass of the physical hardware disposed within the nacelle. Such costs may be reduced by minimizing the size and mass of, for instance, the drivetrain, the generator system, as well as any housing assemblies and support structures therefor. One way to reduce the size of a wind turbine generator is to increase the operating or drive speed of the generator. Furthermore, in order to increase the generator speed, some form of a speed increaser or related gearbox is required to convert typically low rotational speeds of the main shaft into a higher speed suitable for driving a relatively small generator. While prior advances have led to certain accommodations for such implementations, there is still much room for improvement.
In a conventional gearbox, a relatively small number of gear teeth are meshed between gears so as to communicate an input torque at a drive gear to an output torque at a driven gear. In the presence of substantially high rotational torque as with wind turbine applications, however, the gear teeth are continuously subjected to significant levels of localized forces and stresses during normal operation. As a result, the physical size and mass of the hardware, including the gear set, associated housing assemblies and support structures of speed increasing gearboxes, must be sufficiently large to accommodate for such forces, which undesirably adds to the overall cost. Furthermore, such gearbox installations are relatively more susceptible to gear misalignment. In wind turbine applications, large loads received in response to strong and/or sudden gusts of wind, for example, may directly and negatively impact gear alignment. As such, currently existing systems critically require precise bearing locations on the input stage of the wind turbine as well as stiffer, or larger and heavier, gearbox housing assemblies in order to sufficiently compensate for such high loads. However, providing such measures further adds to the size and mass of the gearbox and the drivetrain, which in turn, further adds to the overall cost of implementation.
Accordingly, it would be beneficial to provide a drivetrain which reduces the costs associated with manufacturing, implementing and maintaining wind turbines while improving upon or at least maintaining the performance and efficiency of currently existing installations. Moreover, there is a need for a drivetrain for a wind turbine which combines a more efficient and reliable first stage speed increaser with a lighter and more cost-effective second stage speed increaser. In particular, there is a need for a friction-based first stage speed increaser which eliminates the need for large generators and increases the tolerance to misalignment without compromising performance or efficiency. There is also a need for a first stage speed increaser which distributes large rotational torque over a wider area so as to eliminate localized stresses on components of the drivetrain. Furthermore, there is a need for a second stage speed increaser which eliminates the need for a relatively large gearbox and is adapted for use with smaller, more conventional gearbox assemblies.